1. Field of the Invention
The present invention relates to a method for setting-up a program profile in the control of the injection speed of injection molding machines and an apparatus therefor.
2. Related Art
In injection molding machines, the control of the moving speed of the injecting plunger (screw) in a forward direction is usually conducted in accordance with a program profile, which is preliminarily set up in a computer.
The profile is generally set up in the computer in such a manner that a filling stroke of the injection plunger is divided into a plurality of phases, and the moving speed of the plunger in a forward direction is directly designated at every phase of the stroke to obtain a multi-step rectangular-shaped profile.
FIG. 1 is a graph showing the thus obtained conventional program profile in the control of the moving speed of the injection plunger. As shown in FIG. 1, in the conventional profile, the filling stroke of the injection plunger is divided into five phases, and the moving speed of the plunger V1 to V5 is directly designated at every phase of the stroke to obtain the multi-step rectangular-shaped profile.
In this manner, according to the conventional technique for setting up a program profile in the control of an injection speed of injection molding machines, it is necessary to designate the moving speed of the plunger directly for every divided phase of the stroke of the plunger. However, in actual mold cavities, the cross-section of the course of the melt resin is suddenly changed, so that the conventional rectangular-shaped profile does not correspond to the actual movement of the melt resin as it flows through the mold cavity.
Therefore, according to the conventional technique, in order to obtain a profile which correspond to the actual shape of the course of the melted resin in the cavity, it is necessary to increase the number of the steps of the rectangular portions of the profile; accordingly, the number of the phase to be divided of the moving speed of the plunger should be increased.
Further, it is required to set up the program profile so as to complete to fill up the molding cavity with melt resin within a period as short as possible without disturbing the flowing condition of the melt resin in the mold cavity. Therefore, the program profile should be set up, by which the moving speed of the plunger is changed so as to comply with the actual shape of the course of the melt resin in the mold cavity.
Furthermore, in order to set up such a profile, the know-how on the basis of a molding principle is necessary to control the moving speed of the plunger when the melt resin starts to be injected into a cavity or when the filling up phase of the resin is finished.
Moreover, as shown in FIG. 1 by broken lines, the actual moving speed of the injection plunger in a forward direction has some delays from the profile on the leading and trailing edges thereof when the moving speed is changed. As apparent from FIG. 1, the actual moving speed of the injection plunger does not change according to the multi-step rectangular-shaped profile set up in the computer.
Therefore, the actual profile of the moving speed of he injection plunger (hereinafter referred to as "a prosecuting profile") does not correctly correspond to the program profile in the control of the injection speed (hereinafter referred to as "a set-up profile"), so that the prosecuting profile and the set-up profile are not the same when superimposed on each other when a closed loop control is conducted. In order to solve this drawback, a delay control is applied in which time constants are generated on the leading and trailing edges of the moving speed of the plunger. However, such delayed leading and trailing edges are not involved in the profile.
From these reasons, when a closed loop control is conducted, the prosecution profile is deviated from the set-up profile even if the control is conditioned normally; such a deviation causes difficulty in the control of the moving speed of the plunger.
On the other hand, another method for setting a program profile is suggested where the profile corresponds to the variation of the shape of the course of the melted resin in the mold cavity. According to the method, the profile is formed by broken lines being connected, however, it is difficult to set parameters unless the shape of the course of the melted resin in the mold cavity is well known, and it is required to have many points to be set up in order to obtain the profile which corresponds to the shape of the flowing path of the melted resin. Therefore, according to the method, it would be difficult to realize an idea that the required profile can be obtained with a small amount of inputting data. Further, the know-how for setting the parameters is much more difficult than that for setting a multiple rectangular-shaped profile.